Larson Davis Spartan 821, Справочное руководство

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Spartan 821/721 Manual Glossary C-17
The sound pressure is squared and averaged over a fixed time period. Unlike the moving
average, the sound pressures in all time intervals are equally weighted.
Sound Pressure Level (SPL, Lp)
The logarithmic form of sound pressure. It is also expressed by attachment of the word
decibel to the number. The logarithm is taken of the ratio of the actual sound pressure
to a reference sound pressure which is 20 Micro-pascals (  Pa). There are various
descriptors attached to this level depending on how the actual sound pressure is
processed in the meter:
Instantaneous
: The time varying reading on a meter face on in a meter output due to
changes in the sound pressure. The reading will depend on the time-weighting applied.
The fundamental relationship between the two is logarithmic
where p
0
is the reference sound pressure of 20 µPa. The square of the sound pressure is
a power-like quantity that can be expressed in the original form of the level definition
Sound Pressure Level can be converted to sound pressure as follows. If the sound
pressure is 1 Pascal, then the sound pressure level is
Calibrators often use a level of 94 dB so they generate a sound pressure of 1 Pascal.
If the sound pressure level = 76.3 dB, then the sound pressure is
Energy Average (L
eq
)
: The value of a steady sound measured over a fixed time period
that has the same sound energy as the actual time varying sound over the same period.
This descriptor is widely used. It is a fixed average. See Sound Pressure
Impulse : The value of an impulsive sound. The reading will depend on the time-
weighting applied.
Unweighted Peak : The peak value of a sound with a meter that has flat frequency
weighting and a peak detector.
Weighted Peak : The peak value of a sound with a meter that has a frequency weighting
other than flat and a peak detector.
Sound Power (W)
The sound power emitted by a sound source. It is measured in Watts.
Sound Power Level (PWL, Lw)
The logarithmic form of sound power. It is also expressed by attachment of the word
decibel to the number. The logarithm is taken of the ratio of the actual sound power to a
Lp 20log10
prms
p0
------------
= prms p010
Lp 20 
=
Lp 10log10
prms
2
p0
2
------------
= prms
2
p0
210
Lp 10 
=
L
p
20log
10
1
20 10
6 –

----------------------
20log
10
50000
 
20 4.699
 
94.0dB = = = =
Pa 20 10
6 –
 10
76.3 20

 20 10
3.815 6 –
 20 10
2.185 –
 20 0.0065   0.13 = = = = =